Chemical changes associated with ocean acidification can affect the physiological processes underlying performance of aquatic organisms. The interaction of the ocean’s multifaceted carbonate system with numerous biological pathways makes teasing out mechanisms very complex. Traditionally, whole-organism metrics of performance, such as growth, have been used to estimate the net biological effect of these mechanistic factors. Using this metric, we hypothesized that under high CO2/low pH conditions, animals would experience an increased energetic demand leading to decreased growth. Natural pH fluctuations in tidally-driven nearshore areas make intertidal animals model organisms for understanding pH tolerance. We subjected the intertidal snail Nucella ostrina to six different levels of seawater pH, ranging from 7.0 to 8.0 on the total scale (pCO2 5892-288 μatm), in indoor aquaria at the Ocean Acidification Environmental Laboratory of Friday Harbor Labs. We measured snail consumption of its barnacle prey and snail shell and tissue growth over 6 wk. We were surprised to observe that with decreasing pH, snails consumed more barnacles. Snails in the pH 7.0 treatment consumed nearly 50% more than snails in the ambient treatment (pH 7.8). Snail growth was similar in all treatments, with a trend towards reduced growth at pH 7.0. At low pH, growth was inhibited relative to food intake. We inferred that unmeasured costs associated with ocean acidification outweighed benefits. If snail feeding increases with reduced pH due to ocean acidification, the interaction strength between this snail and its barnacle prey may be increased. However, this increase in predation would not benefit the snail as it does not yield higher growth.